A device for producing fibers or microfibers

ABSTRACT

A device for producing nanofibers or microfibers from solutions, emulsions, liquid suspensions or melts containing a spun substance, comprises a chamber in which a hollow shaft is assembled, on which at least one rotating disc with an output gap is mounted, The chamber is generally provided with a source of the flowing gas and a collection area. In an alternative embodiment, the chamber is provided with a number of side by side arranged hollow shafts. 
     It is preferred that at least one hollow shaft is provided with two superposed rotating discs. At least one rotating disc is composed of two successive parts, wherein between the upper part and the lower part an outlet gap is formed around the circumference thereof. The size of the outlet gap between the upper part and the lower part of rotating disc may be formed by a spacer element, in particular a spacer ring.

TECHNICAL FIELD

The invention relates to a device for producing nanofibers ormicrofibers from solutions, emulsions, liquid suspensions or meltscontaining a spun substance.

BACKGROUND ART

Currently there are numerous devices for electrostatic spinning ofsolutions, emulsions, liquid suspensions or melts containing a spunsubstance. Described are systems producing nanofibers comprising bothnozzle and nozzleless arrangements. These devices are structurallydemanding and their operation has a number of shortcomings, includingclogging of nozzles, which leads to an interruption of the operation orreduction in productivity.

As far as the nozzleless devices are concerned, the formation ofnanofibers occurs directly from the surface of spun solutions which canbe in the form of a thin film. Two-layer systems are also used, whereinthe lower layer is formed by a ferromagnetic suspension and the upperlayer by a solution of spun polymer. After application of the magneticfield, sharp vertical cones of the ferromagnetic liquid are formed thatserve as nuclei from which the nanofibers are produced.

Other device is based on the aeration of a spun polymer solution inorder to create a high concentration of bubbles on the surface of thesolution, wherein a lowering of the surface tension takes place and thehubbies form seeds of nanofibers created by virtue of the electricfield.

Another device is based on a slowly rotating cylinder which is partiallyimmersed in a solution of the spun polymer. During the rotation of thecylinder, a deposit of a specific amount of the solution on the rollertakes place, resulting in a formation of a continuous film from which onthe upper part by virtue of a strong electric field so-called Taylorcones serving as nuclei of nanofibers are formed.

Electrostatic spinning methods are characterized by a low speed of theprocess; they are technically complicated and expensive. Theelectrostatic spinning is limited by the necessity of a high voltageelectric field.

There are also devices used that are not based on the application ofelectrospinning. For the formation of nanofibers, these usually takeadvantage of centrifugal force or a gas stream. A rotating disk is used,on the surface of which a thin film of spun solution is produced bymeans of the centrifugal force.

SUMMARY OF THE INVENTION

Said disadvantages of the devices for producing fibers or microfibersfrom solutions emulsions, liquid suspensions, or melts containing spunsuspension can largely be removed by means of the solution according tothe invention whose principle consists in that it comprises a chamber inwhich a hollow shaft is assembled, on which at least one rotating discwith an output gap is mounted. The chamber is generally provided with asource of the flowing gas and a collection area. In an alternativeembodiment, the chamber is provided with a number of side by sidearranged hollow shafts on which rotating discs are mounted.

It is preferred that at least one hollow shaft is provided with twosuperposed rotating discs. At least one rotating disc is composed of twosuccessive parts, wherein between the upper part and the lower part theoutlet gap is formed around the circumference thereof. The size of theoutlet gap between the upper part and the lower part of rotating discmay be formed by a spacer element, in particular a spacer ring.

It is preferred that at least one part of the rotating disc has afrustoconical shape. At least one rotating disc may be provided with apressure element, such as pressure nut. At least one disc or discsdisposed in a chamber which is made of heat resistant material may beprovided with means for their heating.

The inner space of the hollow shaft is connected with the output gap ofeach of the rotating discs by means of openings and at the other endwith a rotary unit for supplying the polymer and further with the drivemotor.

The source of the flowing gas in the chamber is a compressor or a fan.The collecting area can be either a movable conveyor made of abreathable fabric or a rotating collector or a bag of a porous mesh. Thecollecting area may be electrically charged.

The present invention in comparison with the current state of the artprevents drying films of polymer solutions on the surface of rotatingdiscs, it reduces the amount of defects of produced nanofibers andmicrofibrous layers, especially drops. It facilitates the centrifugalspinning of melts, because there occurs no cooling of the melt on thesurface of the rotating elements.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the device for producing nanostructured andmicrostructured materials is shown in enclosed drawings, wherein

FIG. 1 shows an overall diagram of the entire device,

FIG. 2 shows a spindle with a hollow shaft and a disc in the perspectiveillustration and partial longitudinal section,

FIG. 3 shows a specific embodiment of the disc according to theinvention without a spacer and

FIG. 4 shows a specific embodiment of the disc according to theinvention with a spacer.

DETAILED DESCRIPTION OF THE INVENTION Example 1 Preparation of Nano- orMicrofibers from a Polyvinyl Alcohol Solution

To prepare polyvinyl alcohol micro- or nanofibers, a commercial solutionof polyvinyl alcohol Sloviol R16, 16% (wt./Wt.) of solid content(Fichema) was used. The polyvinyl alcohol solution was pumped from thefirst liquid reservoir 17 by the first pump 18 through a connecting hose19 via the first safety valve 20 and the first check valve 21 at a rateof 2-12 ml/min., and fed through an inlet 22 of liquid into the rotationunit 10 from which it further entered into a hollow shaft 3 disposed ina tube 5 of a spindle. Via openings 16 was the polyvinyl alcoholsolution sprayed from the inner space 6 of the hollow shaft 3 into theinner space of the rotating disc 2 having a conical shape with adiameter of 120 mm, between the upper part 7 and the lower part 8thereof The output gap 4 of the conical disc 2 was set up using a spacerring 13 on the width of 200 micrometers as shown in FIG. 4, The rotatingdisc 2 was positioned over the base plate 23 with channels 32 for thedistribution of the drying gas into the chamber 1 in the form of a tube5 of a plexi-glass having the diameter of 35 cm and the height 40 cm. Inthe base plate 23 entered at a rate of 0.7 m³/s drying air preheated toa temperature of 25° C. from a source 11, which is formed by acompressor and a heater. The rotating disc 2 with the hollow shaft 3 wasrotated via an intermediate transmission 15 by means of a drive motor 14at a speed of 1 to 5000 revolutions per minute. The stream of preheatedair carried away the nano- or microfibers generated by the centrifugalforce on the edge of the outlet gap 4 into a collection chamber 12provided with an orifice having a width of the slot 24 of 5 cm and alength of 35 cm and a sliding belt 25 formed by a permeable nonwovenSpunbond having a basis weight 18.8 g/m². The shift velocity was 10cm/min. The nano- or microfibers were stored in the form of a continuouslayer on the surface of the sliding belt 25 of the permeable nonwoven.

At a constant flow of the polyvinyl alcohol solution 10 ml/min,increased a rate of fiber formation with an increasing rotational speedof the disc in the range 1 to 3,000 revolutions per minute. Upon furtherincreasing the rotation speed, the rate of the fiber formation did notfurther increase and the incidence of defects in the fibers network hasincreased in the form of droplets. Therefore, further experiments werecarried out at a rotation speed of 3000 revolutions per minute. At thisspeed of rotation and other conditions described above has increased thebasis weight of the fibers in a linear manner within the range of thepolyvinyl alcohol solution flow from 2 to 8 ml/min. Maximum productivitywas observed at the flow rate 10 ml/min, Further acceleration of theflow to 12 ml/min, under the conditions described. above seemed to becounter-productive already, because neither the fiber formation nor theexploitation of polyvinyl alcohol increased, conversely, they have evenslightly declined. At the same time the incidence of defects in the formof microdroplets has increased. Under these conditions, it appeared asoptimal the flow in the range of 8-10 ml/min. Under these conditions,the basis weight of the layer of polyvinyl alcohol fibers was in therange of 7-10 g/m². Maximum speed of the fiber formation at a flow rateof 8 ml/min., and a speed of rotation of 3000 revolutions per minute was20 g per hour. The distribution of the nanofibers was homogeneous bothin the microscopic and macroscopic level across the whole belt width,which represented 35 cm. The diameter of the majority of fibers observedwas in the range of 400 to 800 nanometers.

The above procedure was repeated with the exception that two rotatingdiscs 2 of the same construction, located on one hollow shaft 3superimposed with a spacing of 10 cm were used, and the flow rate of thepolyvinyl alcohol solution and the shift of the belt 25 of permeablenonwoven were doubled. Under these conditions the rate of the fiberformation at a flow rate of 16 ml/min and the rotation speed of 3000revolutions per minute managed to increase to 38 g per hour. There wereno significant changes in the basis weight of the fibers and theirquality.

Example 2 Preparation of Nano- or Microfibers from Polyamide 6

For the preparation of micro or nanofibers polyamide 6 were used pelletsof polyamide 6 (Rhodin Technyl). From these pellets was prepared asolution 15% (wt./wt.) in 85% (wt./wt.) formic acid (Penta) at atemperature of 80° C. This solution was pumped from the first liquidreservoir 17 by the first pump 18 through the connecting hose 19 via thefirst safety valve 20 and the first check valve 21 at a rate of 6-16ml/min., and fed through the inlet 22 of liquid into the rotation unit10 from which it further entered into the hollow shaft 3 disposed in thetube 5 of the spindle. Via openings 16 was the polyamide 6 solutionsprayed from the inner space 6 of the hollow shaft 3 into the innerspace of the rotating disc 2 between the upper part 7 and the lower part8 thereof. The disc 2 having a conical shape with a diameter of 120 mmprovided with the pressure element 9 in the form of a nut was used, asit can be seen from FIG. 3. The pressure of the presser nut wasgradually changed so that an opening of the outlet gap 4 occurs at apressure in the range of 4-400 bar. The rotating disc 2 was positionedover the base plate 23 with channels 32 for the distribution of thedrying gas into the chamber 1 in the form of a tube 5 of a plexi-glasshaving the diameter of 35 cm and the height of 40 cm. In the base plate23 entered at a rate of 0.6 m³/s drying air preheated to a temperatureof 35° C. from a source 11, which is formed by a compressor and aheater. The rotating disc 2 with the hollow shaft 3 was rotated via anintermediate transmission 15 by means of a drive motor 14 at a speed of1 to 5000 revolutions per minute. The stream of preheated air carriedaway the nano- or microfibers generated by the centrifugal force on theedge of the outlet gap 4 into a collection chamber 12 provided with anorifice having a width of the slot 24 5 cm and a length 35 cm. At aheight of 5 mm above the slit 24 of the aperture, a rotating collectorof fibers in the form of a roller made of fine steel mesh having adiameter of 10 cm and provided with a motor imparting the collector arotation of 10 rpm., was positioned longitudinally horizontally.

Nano- or microfibers were deposited evenly over the whole surface of therotary collector in the form of a continuous layer of a thickness ofalmost 3 mm in the form resembling a soft cotton wool. When increasingthe pressure in the interior of the disc between the upper part 7 andthe lower part 8 thereof, a reduction in diameter of the fibers hasoccurred. While at a pressure of 4 bar the fiber diameter was in therange 600 to 900 nm, at a pressure of 400 bar the diameter was alreadyin the range of 200 nm to 400 nm. The rate of the fibers formation wasin the range of 50 g to 135 g per hour, depending on the conditions. Theoptimal flow rate was 14 ml/min.

In another experiment, a chamber 1 made of plexi glass and having acuboidal shape with a length of 2 m and a width and a height of 50 cmwas used, in which two rotating discs 2 were placed side by side, withpressure elements 9 in the form of nuts. The discs 2 were placed at adistance of 1 m apart. Optimal conditions were used for spinning thepolyamide 6 solution as identified in the above described experiment.The flow in each disk was 14 ml/min. The pressure in the inner space ofthe disk ? between the upper part 7 and the lower part thereof was 60bar. The collection of the fibers in the collecting space 12 was carriedout using a slot having a width of the aperture 24 of 20 cm and a lengthof 2 m and a sliding belt 25 of the permeable Spunbond nonwoven having abasis weight of 18.8 g/m2, also with a width of 2 m. The speed ofdisplacement of the belt was 10 cm/min. The nano- or microfibers havebeen stored in the form of a continuous layer on the surface of the belt25 of a permeable fabric. The distribution of the nanofibers washomogeneous both in the microscopic and macroscopic level across thewhole belt width, which represented 35 cm. The diameter of the majorityof fibers observed was in the range of 400 to 800 nanometers. The basisweight of the fibers was in the range of 4-6 g/m².

Example 3 Encapsulation of Probiotic Bacteria into Gelatin Microfibers

For the encapsulation of probiotic bacteria, a 10% (wt./wt.) suspensionof the microbial preparation BA (1.10⁹ CFU/g) (Milcom) containing theprobiotic strains of genera Lactobacillus acidophilus andBifidobacterium bifidum freeze-dried with powdered milk in distilledwater was used. Further, a solution of 30% (wt./wt.) of pig skingelatin, 300 bloom, type A (Sigma-Aldrich) in 40% (vol./vol.) aceticacid was used. The gelatin solution at a temperature of 45° C. waspumped from the first reservoir 17 of liquid by means of the first pump18 via the first connecting pipe 19 through the first safety valve 20and the first check valve 21 at a rate of 5 ml/min. Simultaneously, abacterial suspension was pumped from the second reservoir 26 of liquidby means of the second pump 27 via the connecting hose 19 through thesecond safety valve 28 and the second check valve 29 at a rate of 5ml/min. The gelatin solution and bacterial suspension were mixed in amixing chamber 30 having a volume of 5 ml. The resulting bacterialsuspension in the gelatin solution was fed through the inlet 22 ofliquid into a rotation unit 10 from which it further entered the hollowshaft disposed in the tube 5 of the spindle. Through the openings 16,the suspension was further sprayed from the inner space 6 of the hollowshaft 3 into the inner space of the rotating disc 2 of a conical shapewith a diameter of 120 mm, between its upper part 7 and the lower part8. The output gap 4 of the conical disc 2 was set using the spacerelement 13 to the width of 150 microns, as shown in FIG. 4. The rotatingdisc 2 was positioned over the base plate 23 with channels 32 for thedistribution of the drying gas into the chamber 1 in the form of a tubemade of fine steel mesh 35 cm in diameter and the height 40 cm. Into thebase plate 23 entered the drying air preheated to a temperature of 40°C. from a source 11, which is formed by a compressor and a heater, at avelocity of 0.8 m³/s.

The rotating disc 2 with the hollow shaft 3 was rotated via anintermediate transmission 15 by means of a drive motor 14 at a speed of3500 revolutions per minute. The stream of preheated air carried awaythe nano- or microfibers generated by the centrifugal force on the edgeof the outlet gap 4 of the rotating disc 2 into a collection chamber 12provided with an orifice having a width of the slot 24 of 10 cm overwhich a bag made of a permeable nonwoven Spunbond having a basis weight18.8 g/m². The shift velocity was 10 cm/min. The microfibers were storedin this bag in the form resembling a soft cotton wool.

The yield was 80 g of the microfibers with the encapsulated bacterialculture in one hour of the operation. A microscopic analysis confirmedthe presence of bacterial cells encapsulated within the microfibershaving a diameter of between 5 and 10 microns. Standard methods formicrobiological analysis showed that there was only a small decrease invitality of the original bacterial culture, expressed as a number ofcolony-forming units (CFU), by one order, Microbiological testsconfirmed a significant protective effect of the encapsulating against asimulated acidic environment of the stomach and against the action ofbile acids.

Example 4 Preparation of Fibers from the Melt the Polyhydroxyalkanoate

A melt of polyhydroxy alkanoate (Nanjing Huichen Co., Ltd., China) wasprepared in the first reservoir 14 of a solution equipped with aninduction heating, and maintained at a temperature of 300 degreesCelsius. The entire device was thermally insulated.

The melt was pumped from the first reservoir 17 of a solution by thefirst pump 18 via the insulated connecting hose 19 made of a profiledsteel strip through the first safety valve 20 and the first check valve21 at a velocity of 10 ml/min., and fed through the inlet 22 of a liquidinto the rotation unit 10 from which it further entered into the hollowshaft 3 disposed in the tube 5 of the spindle. Through openings 16 werethe melt sprayed from the inner space of the hollow shaft 6 into theinner part of the rotating disc 2 of a conical shape, with a diameter of120 mm, between the upper part 7 and the lower part 8 thereof. Theoutput gap 4 of the conical disc 2 has been set using the spacingelement 13 to the width of 50 microns, as it is apparent from FIG. 4.The rotating disc 2 was positioned over the base plate 23 equipped withchannels 32 for the distribution of the drying gas into the chamber 1 inthe form of an insulated steel tube having the diameter of 35 cm and theheight of 40 cm. Into the base plate 23, the drying air preheated to250° C. from a source 11, which was formed by a compressor and a heater,entered at a velocity of 1 m³/s. The rotating disc 2 with the hollowshaft was rotated via an intermediate transmission 15 by means of adrive motor 14 at a speed of 1 to 5 000 revolutions per minute. Thestream of preheated air carried away the nano- or microfibers generatedby the centrifugal force on the edge of the outlet gap 4 into acollection chamber 12 provided with an orifice having a width of theslot 24 of 5 cm and a length of 35 and a sliding belt made of a finesteel mesh.

The basis weight of the fibers was in the range of 8-10 g/m². Thedistribution of the nanofibers was homogeneous both in the microscopicand macroscopic level across the whole belt width, which represented 35cm. The diameter of the majority of fibers observed was in the range of400 to 800 nanometers. The rate of fibres production was 600 g per hour.

INDUSTRIAL APPLICABILITY

Due to preventing the drying of films of polymer solutions on thesurface of rotating discs and a reduced quantity of defects fibrouslayers, a device for the production of fibers or microfibers fromsolutions, emulsions, melts or liquid suspensions containing a spinnablepolymer according to the invention may be advantageously used to producenanofibers or microfibers, where a high productivity work is required.The device also facilitates the centrifugal spinning of melts, becauseno cooling of the melt on the surface of the rotating elements takesplace.

LIST OF REFERENCE NUMBERS

1—chamber

2—disc

3—hollow shaft

4—output gap

5—tube

6—inner space

7—upper part

8—lower part

9—pressure element

10—rotary unit

11—source of the gas flow

12—collection area

13—spacer element

14—drive motor

15—intermediate transmission

16—openings

17—first reservoir

18—first pump

19—connecting hose

20—first safety valve

21—first check valve

22—liquid inlet

23—base plate

24—slot

25—sliding belt

26—second reservoir

27—second pump

28—second safety valve

29—second check valve

30—mixing chamber

31—heating device

32—channel for gas distribution

1. A device for producing nanofibers or microfibers from solutions,emulsions, liquid suspensions or melts containing a spun substance,wherein it comprises a chamber in which a hollow shaft is assembled onwhich at least one rotating disk with an output gap is mounted.
 2. Thedevice for producing nanofibers or microfibers as defined in claim 1,wherein the chamber is provided with a source of the gas flow and acollection area.
 3. The device for producing nanofibers or microfibersas defined in claim 1, wherein the chamber is provided with a number ofside by side arranged hollow shafts on which rotating discs are mounted.4. The device for producing nanofibers or microfibers as defined inclaim 1, wherein that at least one hollow shaft is provided with atleast two superimposed rotating discs.
 5. The device for producingnanofibers or microfibers as defined in claim 1, wherein least onerotating disc is composed of two successive parts, wherein between theupper part and the lower part an outlet gap is formed around thecircumference thereof.
 6. The device for producing nanofibers ormicrofibers as defined in claim 5, wherein the size of the outlet gapbetween the upper part and the lower part of the rotating disc is formedby a spacer element, for example a spacer ring.
 7. The device forproducing nanofibers or microfibers as defined in claim 1, wherein atleast one part of the rotating disc has a frustoconical shape.
 8. Thedevice for producing nanofibers or microfibers as defined in claim 1,wherein at least one rotating disc is provided with a pressure element.9. The device for producing nanofibers or microfibers as defined inclaim 6, wherein the pressure element is a pressure nut.
 10. The devicefor producing nanofibers or microfibers as defined in claim 1, whereinthe inner space of the hollow shaft is interconnected via openings withthe inner space of each of the rotating discs between their upper partand the lower part and the output gap.
 11. The device for producingnanofibers or microfibers as defined in claim 1, wherein the hollowshaft is interconnected with a rotary unit allowing the supply of aliquid or a melt comprising the spun substance, and further with a drivemotor.
 12. The device for producing nanofibers or microfibers as definedin claim 1, wherein the source of the gas flow in the chamber is acompressor or a fan.
 13. The device for producing nanofibers ormicrofibers as defined in claim 2, wherein the collection area is amovable conveyor made of a nonwoven fabric or a rotating collector or abag of a porous mesh.
 14. The device for producing nanofibers ormicrofibers as defined in claim 2, wherein the collection area iselectrically charged.
 15. The device for producing nanofibers ormicrofibers as defined in claim 1, wherein the rotating disc or discslocated in the chamber, made of a heat resistant material, are fittedwith means for their heating.